Cluster-configuration-interaction analysis of Cu 2p and valence-band photoemission measurements on Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 superconductors

Abstract

The electronic structure of Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 high-Tc superconductors is investigated by Cu 2p x-ray photoemission spectroscopy and valence-band resonant photoemission at the Cu L3 edge. The data suggest strong correlation effects for the Cu 3d electron states due to a large on-site Coulomb interaction. By means of a simplified cluster-configuration-interaction model we derive the model Hamiltonian parameters which quantify the Cu d-d interaction energy, the O to Cu charge-transfer energy, and the degree of Cu d–O 2p hybridization. The solutions for the two compounds differ mainly in the charge-transfer energy, which in both cases is lower than the energy required for a Cu d-d charge fluctuation. An energy gap of about 1 eV for both compounds is found. This identifies them as charge-transfer insulators, in analogy with what was already found for CuO and other copper oxide based high-Tc superconductors. The density of states at the Fermi level is assigned to doping induced states in the semiconductor gap.

Source-reported materials — not catalogue approval

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